1. Field of the Invention
The present invention relates to a motor-drive device for sensors around a spherical electromagnetic lens, for example a Luneberg type lens using in a system of transmission and/or reception. The invention can be applied especially to receivers and/or transmitters carrying out multiple-satellite tracking, for example in the field of communications by orbiting satellites.
Satellite communications have become very important. In addition to the commonly used geostationary satellites, there are orbiting satellites, especially for wide-band, high-bit-rate telecommunications, for example for multimedia applications.
2. Description of the Prior Art
It is thus necessary to provide for ground stations that can track several satellites at the same time. The basic techniques to be used are known. A station generally includes a wide frequency band omnidirectional transmission and/or reception device. There are known ways of making a device of this kind by using an electromagnetic spherical lens, for example of the Luneberg type, associated with mobile microwave sensors in the immediate vicinity of the lens surface. Through an appropriate disposition of the index gradient of the constituent material of the lens, it is possible that a microwave parallel beam striking the upper face of the lens, oriented skywards, will converge by incurvated rays towards the point diametrically opposite the point at which the normal to this beam is tangential to the sphere. A microwave sensor held in the vicinity of this diametrically opposite point picks up the wave of this beam coming, for example, from a satellite.
As a rule, a transmission and/or reception device designed for multiple-satellite tracking must follow at least two orbital satellites at the same time. These satellites are redundant, namely they provide the same information traffic. When, as a result of the orbiting, one of the satellites being tracked goes out of sight, for example by vanishing over the horizon, the transmission and/or reception device switches over to the other satellite. The transmission and/or reception device thus has at least two microwave sensors as well as means to control the position of the sensors as a function of the information available on the position of the satellites to be targeted.
Since the sensors have to move in the vicinity of the entire inner surface of the spherical lens, it is useful to provide for a suitable motor-drive mechanism. Known mechanisms make use of systems of circular rails rotating around the lower half sphere. The sensors move on these circular rails. These mechanisms require several electrical motors. They require at least one motor to make the rail rotate, and one motor per sensor. The result is a complex and costly mechanism. The high cost arises especially from the cost of the electrical motors. The complexity of the system as well as the relative reliability of the motors lowers the overall reliability of the motor-drive assembly.
It can be seen therefore that prior art motor-drive systems for sensors in a receiver and/or transmitter with spherical lens have at least two drawbacks, firstly high cost and secondly, lack of reliability. These two drawbacks are especially very troublesome for multimedia applications, namely large-scale consumer applications. In applications of this type, a receiver and/or transmitter is placed for example on the roof of a dwelling, and it is not desirable to have to make frequent emergency repairs to a motor-drive system. The reliability of this system is therefore very important and, obviously, so is the competitive cost of this receiver and/or transmitter as a whole.
It is an aim of the invention to overcome the above-mentioned drawbacks. To this end, an object of the invention is a motor-drive device for transmission and/or reception modules in a receiver and/or transmitter with spherical electromagnetic lens, this device comprising, for each module, at least one piezoelectric motor rigidly connected to the module. The module moves in the vicinity of the surface of the lens by the reptation of the piezoelectric motor on this surface.
An object of the invention is also a receiver and/or transmitter with spherical electromagnetic lens using a device of this kind.
The main advantages of this invention are that it brings a reduction in the weight of transmission and/or reception device with Luneberg lens and improves the electrical and microwave performance characteristics of such a device.